Electrophoresis display (EPD) technology has become one of the electronic display techniques that have great potential due to the combination of the advantages of usual paper and electronic displays. Electrophoresis display is usually bicolor, that is, only two different colors such as black-white, red-blue and the like can be displayed. Therefore, since development of color electrophoresis display not only can satisfy the demand for colorization, but also has great economic benefits, it will necessarily be the direction for future development of electrophoresis display.
Currently, methods for achieving the colorization of electrophoresis display include additional attaching color filter film, controlling the electrophoresis rate, and increasing sub-pixels.
The color filter method achieves color display by additionally attaching a layer of color filters on the surface of the upper transparent electrode substrate of a bicolor electrophoresis display, with black intervals between color filters to avoid color cross-talk. Although the color electrophoresis display thus formed has a high resolution, the color filters in this method causes a loss of about 70% of reflective light, which greatly affects the color saturation of images, resulting in a very dark display screen under conditions of weak light.
In the method of controlling electrophoresis rate, pigment particles of three different colors and having different Zeta potentials are suspended in a transparent electrophoresis solution, and the particles are conferred different electrophoresis rate by application of an electric potential, thereby achieving color display. It is relatively simple and convenient to prepare a color display with the method of controlling electrophoresis rate, but it is difficult to precisely control the Zeta potentials of the three pigment particles, resulting in the difficulty to achieve high contrast and brightness for the image.
The sub-pixel method utilizes microencapsulation techniques to encapsulate electrophoresis solution comprising three pigment particles of different colors (such as red, green and blue), respectively, to form microcapsules displaying different colors. Subsequently, with a radiation curing material as a binding agent, first microcapsules of one color (such as red microcapsules) are coated on a substrate with an electrode substrate formed upon, which is subject to selective ultraviolet light exposure curing with a photomask, and then the cured microcapsules are partly removed by a solvent that can dissolve the radiation curing material, therefore disposing the red microcapsules on specific positions on the substrate comprising electrode plates. By repeating the aforementioned steps, the green and blue microcapsules can be arranged on the electrode plates in an orderly manner. For the prepared display, color display can be achieved by adjusting the electric potentials across the electrode plates. Although a good display effect can be obtained, this microcapsule coating process is complicated, requires repeated exposure processes and solvent soaking processes, which greatly damage the microcapsules, and has a low yield.
US Patent Application US 20030021005 disclosed an electrophoresis display with color filters. Although this technique can realize colorization, it reduces the light reflectivity of the display, which affects the display effect.
Although colorization is enabled by the technical means of disposing color filters on the microcapsules, the light has to pass through in and out the color filters and the microcapsules during incidence and reflection, that is, the light has to pass through four membrane layers. Therefore, the light loss is great. The light reflectivity is reduced to 35%, even down to 20%. When light is weak, the shade contrast is significantly reduced.
U.S. Pat. No. 6,583,780 disclosed an implementation of a color microcapsule electrophoresis display. This technique primarily employs the method of photolithography technology, which requires repeated etching operations and thus is complicated, hard to control, and has low maneuverability. Meanwhile, the etching causes great damages on the microcapsules and it is difficult to ensure the quality of the microcapsules and the display effect of the display.